Paris, 8 December 1997

Millennium Star Atlas marks the completion of ESA's Hipparcos Mission

The European Space Agency announces the completed publication of its monumental positional survey of the celestial sphere, representing the most substantial improvement of astronomers' knowledge of the distribution of stars within our Galaxy ever achieved. Construction and publication of the Hipparcos and Tycho Catalogues, the final products of ESA's Hipparcos space astrometry mission, have occupied European scientific teams since the launch of the Hipparcos satellite in 1989. These results have at least ten times the accuracy of all previous sky surveys.

This vast stellar census has been available to the world's astronomers since June, through ESA's Hipparcos world wide web site, various stellar data centres, and the wide distribution of the multi volume catalogue. While the printed catalogue bears a superficial resemblance to a telephone directory, with page after page of closely spaced numbers, one of the most remarkable highlights is the final three volumes containing actual maps of the sky, recently completed and now being distributed. These have been produced through a unique collaboration between the European Space Agency, the Hipparcos Project, and Sky Publishing Corporation of Cambridge, Massachusetts, USA (the publishers of the monthly popular astronomy magazine Sky & Telescope). The three volumes appear simultaneously in the larger format 'Millennium Star Atlas' published by Sky Publishing, to serve the ever more demanding needs of both professional and amateur astronomers, and teachers of astronomy.

The Millennium Star Atlas contains 1548 sky charts, depicting the heavens with unprecedented information on the nature of our Galaxy using the stellar information drawn from ESA's Hipparcos and Tycho Catalogues.

The Millennium Star Atlas's coordinator and lead author Roger W. Sinnott of Sky Publishing has worked closely with ESA and the Hipparcos scientific groups for the last two years, leading a team dedicated to the production of the most detailed, comprehensive, and complete star atlas ever undertaken. It shows more than one million stars, three times as many as any other atlas in print. More than 10,000 of the nearest stars are labelled with their distances in light-years, as newly determined by the Hipparcos satellite. The charts also include the locations and rough shapes of 8000 remote galaxies. "Sky Publishing is proud of the results of our close collaboration with the professional scientists who built the star catalogues on which the Atlas is based, and the European Space Agency which had the vision to undertake the highly-successful Hipparcos programme", said Roger Sinnott. "And it does appear that we have achieved our original hopes of serving the ambitious demands of today's amateur astronomers at the same time as providing a rigorous celestial map to the professional users of the Hipparcos satellite data." The limiting magnitude of the Atlas, corresponding to the survey limit of the Hipparcos satellite at around 11th magnitude, reveals stars about 100 times fainter than those visible to the naked eye, and is well-suited to the requirements of the well-equipped amateur star gazer.

The Hipparcos Project Scientist, Dr Michael Perryman, describes the completion of the Millennium Star Atlas by Sky Publishing as a major cartographic achievement, standing alongside the great sky maps of antiquity. "The Atlas succeeds in making the Hipparcos star survey visually dramatic, and brings home the complex and fundamental nature of its measurements" he said.

Professor Roger Bonnet, ESA's Director of Science, places the value of the Atlas in its historical context: "Down through the ages, star maps have served a multitude of needs. Celestial globes and seasonal charts of the night sky, containing a few hundred stars at most, have helped initiate newcomers to astronomy and teach the constellations. Mariners and aviators have located the navigational stars that were once vital for a safe ocean passage. Special finder charts have helped astronomers point their telescopes. When a new comet appears, the discoverer reaches for the most detailed star map available to plot its location among the stars and claim credit for the find. The three final volumes of the printed Hipparcos and Tycho Catalogues, with their 1548 celestial charts, brings these orientational uses of star maps to a new plateau, and brings home the remarkable achievements of the Hipparcos mission."

While the world's astronomers are busily digesting and interpreting the rich scientific harvest from the Hipparcos mission, and are expected to continue doing so for many years, ESA views the Millennium Star Atlas as a fitting end to its formal responsibilities to the Hipparcos mission. "The European Space Agency has completed a most remarkable scientific programme", said Antonio Rodota', Director General of ESA. "In so doing, ESA has succeeded in placing a long-lasting imprint on our progress in understanding our Universe", he said.

The world's astronomers have had access to the massive Hipparcos and Tycho Catalogues since June, when they were made available through ESA's Hipparcos world wide web site, through various stellar data centres, and through the wide distribution of the star catalogues and their various annexes to the professional astronomical community on a collection of CD-ROMs. Starting in June, these catalogues, and their accompanying documentation, have been made available to astronomical observatories and scientific libraries as a 17-volume printed catalogue. Use of the catalogues, and the scientific data contained within them, have already spawned more than 100 published scientific papers since June when astronomers started deciphering the detailed and complex stellar data in what is expected to be a lengthy and highly productive interpretative phase of the Hipparcos results.

Started in 1980 the Hipparcos programme had a single goal: to produce the most accurate positional survey of more than 100,000 stars, pinpointing their locations, and in the process determining their distances, their motions, and other characteristics such as their variability and binary nature. The Hipparcos mission was a major technical challenge for both European industry which built the satellite and the European astronomical community which produced the resulting star catalogues.

The result is that the world's astronomers now have a remarkably sharp three-dimensional view of the distribution of stars in our region of the Milky Way galaxy, which they are using to revise models of stellar structure and Galactic evolution. As a by-product, the positions of the stars in the sky can now, for the first time, be propagated reliably backwards and forwards from the present to give a true impression of how the sky looked to our ancestors thousands of years in the past, or how it will look to our descendents thousands of years in the future.

ESA's Hipparcos www site includes a wealth of information on the results of the Hipparcos mission, including three-dimensional images of our Galaxy as seen by Hipparcos, and several animations including star motions through space measured for the first time by the Hipparcos satellite, variable stars suitable for monitoring by amateur astronomers, and minor planets orbiting the Sun.

For details of the Millennium Star Atlas, see Sky & Telescope's www site.

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